In recent years, the demand for electronic still cameras is expanding in the place of cameras using the silver-salt photographing technology developed since 19th century. In the electronic still camera, “JPEG” is used as a data compression and expansion technique in order to efficiently process image data on the occasions of transmitting and storing the image data. A technical core of the JPEG method lies in the discrete cosine transform (DCT).
Since the compression and expansion of moving image data are also possible according to the JPEG method, there is an electronic still camera using this method, which is equipped with a shooting function of the moving image. The technology in which the moving image data are compressed and expanded in units of frame by the JPEG method is called M-JPEG (Motion-JPEG).
On the other hand, “MPEG” is one of techniques in which to compress and expand multimedia data including moving images. In the MPEG method, the technical core used in the video part lies in motion compensated prediction (MC) and DCT. The coding technique combining MC and DCT is called the hybrid coding technique. It can be said that the MPEG method is the technique in which the MC is combined into the JPEG method.
In the electronic still camera utilizing the MPEG method, it is desired that a snapshot which corresponds to one frame of the moving image can be recorded during the shooting of the moving image; for example, such a technique is disclosed in Japanese Patent Application Laid-Open No. Hei 11-75148. It is known that in this type of electronic still camera there is provided an exclusive-use memory area for use in pushing aside and storing snapshot data. However, in this type of camera, this exclusive-use memory area is not utilized until the snapshot shooting is instructed, so that the effective usage rate of the memory during the shooting of moving image is not enhanced. Making it compact-size and low-cost plays a crucial role in evaluation of merchandise values, and it is admitted that there is a room for improvement in terms of implementing area and cost performance. This is the first problem which the inventor of the present invention recognized.
The second problem which the inventor recognized relates also to the similar room for improvement. Since the photographed snapshot is oftentimes printed on paper medium by using a video printer or the like, high image quality is required. However, when the moving image is recorded with the same high image quality as the snapshot, the memory capacity runs out quickly. Thus, a technique is known in which the still image is recorded at the same pixel density level as that in the shooting of the still image, and the moving image whose pixel density is reduced after performing a filtering processing thereon is recorded. In this conventional technique, however, the edge smoothing of the still image or emphasis processing thereof, for example, and so forth can not be performed, thus a filter circuit needs to be newly provided in order to realize these functions.
The third problem that the inventor recognized relates to the usability of a user at the time of shooting a snapshot. Conventionally, the outcome of the photographed snapshot is confirmed only after the shooting of the moving image is completed, so that there are many occasions where the proper photographing of the snapshot is missed out when the shooting of the snapshot is mistaken. Moreover, provision of two shooting modes for the moving image and snapshot is not likely to become a use-friendly design.